Thanks little bro!! =]
The white shirt is the cornerstone of any man's wardrobe; well, it should be at least. You will find no item in a man's wardrobe more versatile than this one. Wear it with jeans or pants, sneakers or patent-leather loafers - pretty much anything. It's the shirt you go to when you can't find a shirt to wear.
Now I won't go into too much detail about the shirt right now, since there is a lot of details to look into - cuff, collar, shape and material, to name a few - but I can certainly tell you that one of the most important things to consider when getting your first white shirt is making sure that it fits well.
A general rule of thumb when it comes to choosing a size is to consult the shoulder of the shirt. The seam at the shoulder of the shirt should hit the middle of your shoulder. Anything else and the shirt would look ill-fitting.
Also, and perhaps this is a personal preference, go for as slim-fitting a shirt as you can get. That way the shirt won't muffin-top when you tuck it in. (And you are tucking in your shirt, right?) As for the length, the shirt should stop at around the hips - long enough to be able to tuck in, but short enough not to look like a dress.
Worn well enough, the white shirt will take you real far in life - farther than any tiffany-colored buffalo plaid will take you.
(The shirt in the picture is from Dirk Lui, and can be found here.)